Recovery of zinc and nickel from waste phosphate liquor

ABSTRACT

Zinc and nickel are recovered from waste phosphate liquor by solvent extraction. Zinc is first extracted with di-2-ethylhexyl phosphoric acid in an organic diluent. Nickel is then extracted from the raffinate of the zinc extraction with dinonyl naphthalene sulfonic acid in an organic diluent.

United States Patent Powell et al.

[ 51 Mar. 14, 1972 [54] RECOVERY OF ZINC AND NICKEL 3,193,381 7/1965George ..23/3l2 FROM WASTE PHOSPHATE LIQUOR 3,388,967 6/1968 Ramaradhya..23/3l2 P [72] Inventors: Howard E. Powell; Lawrence L. Smith, FOREIGNPATENTS OR APPLICATIONS both of Rolla, Mo.

1,186,833 2/l965 Germany ..23/3l2 [73] Assignee: The United States ofAmerica as represented the Secretary of the Interior PrimaryExaminer-Norman Yudkofl" [22] Filed: 1969 Assistant Examiner-S. T. Emery[21 Appl. No.2 887,689 AttorneyErnest S. Cohen and William S. Brown 52us. c1. ..23/312 R, 23/312 P, 210/38, [5 ABSTRACT 210/40 9 511 110.01..3010 1 1/04, c01 g 9/00, COlg 53/00 Zinc and nickel are ecovered fromwaste phosphate liquor by [58] Field f Search 23 2 R, 312 p 3 ME, 309solvent extraction. Zinc is first extracted with di-Z-ethylhexyl 23/165;21Q/21, 33 40 phosphoric acid in an organic diluent. Nickel is thenextracted from the rafiinate of the zinc extraction with dinonyl [56]References Cited naphthalene sulfonic acid in an organic diluent.

UNITED STATES PATENTS 4 Claims, 1 Drawing Figure 2,992,894 7/1961 Hazen23/312 FEED (AQUEOUS) ORGANQ ZINC ORGANIC EXTRACTION PHASE SEPARATIONORGANIC AQUEOUS ORGANIC I H 50, l

MCKEL ORGANIC STRIP EXTRACTION PHASE PHASE SEPARATION SEPARATION AQUEOUSORGANIC 1711 50 I i NICKEL STRIP PHASE SEPARATION ZINC PHOSPHATE NICKELPRODUCT PRODUCT PRODUCT PAIENTEDIIIIR I4 I972 3,649,220

FEED (AQUEOUS) I ORGANIC zINC ORGANIC EXTRACTION PHASE sEPARATICNCRCANIC AQUEOUS ORGANIC H2504 F I N ORGANIC zINC sTRIP 'CKEL EXTRACTIONPHASE PHASE sEPARATIoN sEPARATIoN AQUEOUS ORGANIC {H2804 NICKEL sTRIPPHASE SEPARATION V V ZINC PHOSPHATE NICKEL PRODUCT PRODUCT PRODUCT INVENTORS HOWARD E. POWELL LAWRENCE L. SMITH ATTORNEYS RECOVERY OF ZINC ANDNICKEL FROM WASTE PHOSPHATE LIQUOR Phosphate coating of metals is widelyused in industry, especially in the manufacture of steel products, forseveral purposes: to provide a base to which paint or enamel willstrongly adhere, for corrosion protection, for lubrication indie-forming operations, and to provide a porous surface that will absorband retain lubricating oil. The phosphating solution consistsessentially of phosphoric acid, a primary phosphate of iron, zinc, ormanganese, and oxidizing agents such as nitrites, nitrates, chlorates,and peroxides. The phosphate coating reaction is based on theinsolubility in water and solubility in acids of most metal phosphates.When steel is contacted with the phosphating solution, iron isdissolved, hydrogen is evolved, and the primary metal phosphates areconverted to insoluble secondary and tertiary phosphates that deposit onand strongly bond to the metal surface.

The wastes from such phosphating operations, which consist of spentphosphating solution and an insoluble sludge, are often discharged tostreams or ground waters. This contributes to stream pollution problems,and also represents large losses of nickel and zinc, as well asphosphates and lesser amounts of copper, manganese and lead. Recovery ofnickel and zinc in useful form from such wastes is not undertaken to anyextent by the metal processing industry.

It has now been found, according to the process of the invention, thatnickel and zinc may be selectively recovered from waste phosphateliquors by means of a specific solvent extraction procedure. Thisprocedure involves initial extraction of zinc with di-Z-ethylhexylphosphoric acid (EHPA) in an organic diluent, e.g., kerosene, followedby extraction of nickel from the raffinate of the zinc extraction withdinonyl naphthalene sulfonic acid (DNSA) in an organic diluent.

The drawing is a flowsheet of the process of the invention.

EHPA exists as a dimer, (RH) in kerosene and the generalized equationfor the Zn extraction reaction is believed to be:

DNSA is believed to exist as a polymer, (RH),, in solution and theequation for the Ni extraction is believed to be:

aq ).r org x-2 1 ora uq Compositions of the waste phosphate liquors mayvary considerably depending on the process from which they are derived.Generally, however, they will consist ofaqueous solutions containingabout 0.5 to 2.5 grams per liter of Ni, 0.5 to 3.5 grams per liter ofZn, 3.0 to 6.0 grams per liter of phosphate as P with smaller amounts ofCu, Mn, and Pb. The pH of the solution will usually range from about 3.0to 3.5. pH values substantially below or above these values may resultin inefficient extraction or undesired precipitation. Use of pH valuesof about 3.0 to 4.0 usually result in more efficient extraction of Zn,while pH values of about 2.0 to 3.0 are more efficient for Niextraction. Any mineral acid, alkali metal hydroxide, or ammoniumhydroxide may be used for initial adjustment of pH, if required;however, phosphoric acid or sodium hydroxide is preferred.

Kerosene is the preferred diluent for extraction of Zn. However, otherconventional organic diluents, or carriers, such as fuel oil, gasoline,or other petroleum products, may also be used. Optimum concentrations ofEHPA vary in the diluent may vary considerably, depending on thecomposition of the waste phosphate liquor, type of diluent used, etc.However, concentrations of from about 5 to 30 volume percent are usuallysatisfactory. The optimum amount of extractant, i.e., EHPA-diluentsolution, used will also very widely depending on the nature of thewaste phosphate liquor and diluent, type of extraction process, desireddegree of removal of Zn, etc. A volume ratio of extractant-to-wastephosphate liquor of about 2:1 to 1:2 is, however, usually satisfactory.

The preferred diluent for Ni extraction is butyl ether, provided the Znhas been substantially completely removed prior to extraction of Ni.Otherwise, another of the diluents disclosed above may be preferred,since butyl ether exhibits a considerable affinity for Zn.Concentrations of DNSA in the diluent will usually range from about 5 tovolume percent,

with the volume ratio of extractant-to-waste phosphate liquor (raffinatefrom Zn extraction) being in the range of about 2:1 to 1:2.

The process of the invention may be utilized as a batch or as acontinuous process. It may be carried out as a batch process in an opencontainer equipped with suitable stirring device and drain opening topermit separation of the phases, such container serving both as mixerand settler cell. The organic phase may be retained in the cell andstripped as in the extraction cycle. As a continuous process,commercially available countercurrent equipment including box type,cascade type, or reciprocating plate are all effective.

Extraction of both Zn and Ni are carried out at room temperature andpressure. A contact time of as little as 1 or 2 minutes for Niextraction and about 5 minutes for Zn extraction is usually sufiicient.However, longer periods, e.g., about 20 minutes or more may be necessaryfor maximum extraction in some cases. Where a batch extraction processis employed, several extraction stages may be required if maximumextraction is desired. Generally, three to five stages will extracteither Zn or Ni almost completely.

Following extraction, both Zn and Ni are recovered from the organicextractant by stripping with an aqueous acid solution. The preferredstripping solution is a dilute, i.e., l5 volume-percent, solution ofsulfuric acid. However, other acids such as hydrochloric may be used forstripping. This treatment also regenerates the EHPA and DNSA, which maythen be recycled for reuse in the extraction process.

The raffinate, following extraction of both Zn and Ni, consists largelyof an aqueous solution of phosphoric acid, sodium phosphate and sodiumnitrate. This solution may be reacted with ammonia, ammonium hydroxideor potassium hydroxide to form a mixed fertilizer material.

The invention will be more specifically illustrated by the followingexample.

EXAMPLE A waste phosphate solution from automobile assembly plantscontaining 1.34 gpl Zn, 1.10 gpl Ni, and 3.8 gpl P0,, was adjusted to apH value of 4.5 by addition of sodium hydroxide. One hundred ml. of thissolution and ml. of extractant comprising 20 volume percent EHPA inkerosene were thoroughly mixed in a 500 ml. separatory funnel bymechanical shaking for a period of 20 minutes. The organic and aqueousphases were then separated. N0 adjustment of pH of the aqueous phase wasnecessary as the extraction of zinc lowered to the pH to 2.4.

One hundred ml. of extractant comprising 8 volume percent of DNSA in a 4to 6 mixture of butyl ether and heptane were mixed with the raft'matefrom the Zn extraction by the same procedure as above. Again, theorganic and aqueous phases were separated.

The organic phases from the preceding steps were then separatelystripped with 100 ml. of 15 percent sulfuric acid by mechanical soakingfor 20 minutes in a 500 ml. separatory funnel. The phases were thenseparated and the aqueous phase analyzed for Zn and Ni, respectively.Results showed that 99.5 percent of the Zn and 98.5 percent of the Niwere extracted.

Repeated extractions according to the above procedures showed that threeand five stages of extraction was sufficient to substantially completelyextract the Zn and Ni, respectively.

What is claimed is:

l. A method for recovery of zinc and nickel from waste phosphate liquor,said liquor consisting essentially of an aqueous solution containing 0.5to 2.5 grams per liter of nickel, 0.5 to 3.5 grams per liter of zinc and3 to 6 grams per liter of phosphate, comprising (1) adjusting the pH ofthe liquor to about 3 to 4 and extracting zinc with an extractantcomprising about 5 to 30 volume percent of di-Z-ethylhexyl phosphoricacid in an organic diluent and (2) adjusting the pH of the raffinalefrom the zinc extraction to about 2 to 3 and extracting 3. The method ofclaim 1 in which the organic diluent in the nickel with an extractantcomprising about 5 to volume ni k l ex r ctionis butyl ether.

percent of dinonyl naphthalene sulfonic acid in an organic The method ofClaim 1 in which both the Zinc n lhe dilu nt, nickel are recovered fromthe organic extractant by stripping 2. The method of claim 1 in whichthe organic diluent in the 5 with a sulfuric acid Solutionzincextractant is kerosene.

2. The method of claim 1 in which the organic diluent in the zincextractant is kerosene.
 3. The method of claim 1 in which the organicdiluent in the nickel extraction is butyl ether.
 4. The method of claim1 in which both the zinc and the nickel are recovered from the organicextractant by stripping with a sulfuric acid solution.